How many wires in a hole in a wall stud?



I also don't see a big problem in just drilling another hole (as you say, properly spaced). The strength of the studs wouldn't be seriously compromised unless you got rediculous about it.
daestrom
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There are no rules on this in the 2005 NEC. As long as you keep the cables separated and not bundled and do not apply fire stopping you can put as many cables through a hole in a stud and will fit. If you apply fire stopping you must derate according to the 2008 NEC.
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In article <37adfe4a-b085-4dd3-a291- snipped-for-privacy@d4g2000prg.googlegroups.com>, alt.engineering.electrical, snipped-for-privacy@electrician2.com says...

Doesn't that seem sorta silly?
-- Keith
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krw wrote:

There seem to be two issues here.
One is that penetrations (holes) in vertical and/or horizontal structural members can provide detrimental airflow and reduce the fire stopping effectiveness of the structure.
Another is that heat buildup in conductors cannot dissipate when surrounded by some fire stopping materials (foam, fiberglass, etc.) and so derating may be appropriate.
Chuck
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alt.engineering.electrical, snipped-for-privacy@no.spam.at.all says...

Irrelevant. The point was that you have to derate if you *ADDED* fire stopping.

Bullshit. We're talking about a 2x4. The center of the thing is only 3/4" from free air and the heat conductor is copper (or aluminum).
I'm not buying either reason.
--
Keith

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krw wrote:

In the NEC, derating of bundled conductors is required, with some exceptions. With fire stopping in hollow spaces, some of those exceptions disappear and you must derate.
The requirements on conductors penetrating walls, studs, floors, etc. with fire stopping all but dictate that the conductors pass through metal conduit.
If you think a bundle of conductors in free air will dissipate heat as well as the same bundle encased in fiberglass or foam, then it is understandable you find the explanation wanting.
Chuck
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alt.engineering.electrical, snipped-for-privacy@no.spam.at.all says...

Which is what I'm saying is silly. If you plug a hole that a bundle of wires through you must derate, but if you don't plug it you don't? You *must* drill *more holes in the fire block? *Damned* silly.

What does "all but" mean?

Through a 2x? No, I don't find the explanation wanting, I find is damned stupid! There has to be something more to the rule than you're saying (or know?).
--
Keith

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krw wrote:

Keith, I think what's confusing you is that the NEC simply doesn't address derating conductors passing through a hole in a 2x4. Anywhere. Period.
The NEC does talk about derating bundled conductors. Multiple conductors in a hole in a stud is a bundle and therefore would have to be derated.
But an exception in the NEC says a bundle doesn't have to be derated if it is less than 24 inches in length.
Another exception applies to nipples less than 24 inches in length (think conduit).
But if the bundle goes through fire stopping, the exceptions don't apply and you do have to derate.
Again, the 2x4 itself never enters into any discussion of derating a bundle of conductors in the NEC. It only addresses bundling, derating, and fire stopping.
Does that help?
Chuck
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The problem is both the Neher McGrath and Samuel Rosch ampacity tables were developed using a heat transfer equation applied to radial heat transfer and not axial heat transfer. Axial heat transfer exceptions for the 24 inch nipple, sealoffs, holes in studs, high heat areas along the run of conductor are the result of various field tests. The copper people did a test for fire stopping that resulted in the derating for cables, etc passing through fire stopping in the 2008 NEC. The issue of installing raceways and cables in polyurethane insulation has still not been addressed. I wrote an article on this several years ago at: http://www.electrician2.com/articles/ampacity.htm
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alt.engineering.electrical, snipped-for-privacy@no.spam.at.all says...

Unless that 2x4 is a fire block. Silly.

See the rest of this discussion. Apparently there is an exception for runs under 24" that doesn't include fire blocks. At some point this cases *more* holes in the fire block. Damned silly.

Unless it's a fire block, then it must be derated.

Well, a nipple less than 24" *is* less than 24", so I guess that works.

So if you come up against that situation you have to drill another hole. That is the silliest thing I've heard in a long time.

It *certainly* does! Fireblocks *are* made out of 2x4s.

Helps clarify that I'm *NOT* missing anything and that the NEC is damned silly! ...and I thought most things in there made sense, if you looked at it from *some* angle.
--
Keith

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krw wrote:

I thought someone in this thread went back to the source for derating for over 2 Romexes in firestop. It was based on "experimentation" that found "temperatures well in excess of their 90 C ratings". Results apparently not published, so the applicability to draft stopping not in the hole, as described by gfretwell, is not know by mere mortals like us. Also not known if the experimentation was reasonable. The requirement could make sense from some angle and is still be silly.
As gfretwell pointed out, the effective limitation is "9 current carrying conductors per hole" since you derate from the 90 C ampacity, but you can only use Romex at a 60 C ampacity.
--
bud--


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| In article <37adfe4a-b085-4dd3-a291- | snipped-for-privacy@d4g2000prg.googlegroups.com>, | alt.engineering.electrical, snipped-for-privacy@electrician2.com says...
|> > I've searched all through my 2005 NEC looking for some guidance as to how |> > many 12/2 circuits I can run through a single 3/4" hole in the wall studs of |> > a house I'm building as a retirement project. I can not find anything about |> > it. I've also asked on several over groups. Is there some rule of thumb or |> > is there an actual regulation that I'm missing. I'm way out in the country |> > and we do not have an inspector that I can ask and the one in the county |> > seat said there is no restriction. I'm not concerned about county |> > restrictions, I'm concerned about safety. |> > |> > TIA |> > |> > -- |> > JC from Gnat Flats |> |> There are no rules on this in the 2005 NEC. As long as you keep the |> cables separated and not bundled and do not apply fire stopping you |> can put as many cables through a hole in a stud and will fit. |> If you apply fire stopping you must derate according to the 2008 NEC. | | Doesn't that seem sorta silly?
No. A simple short (2 inches) hole does not tend to impact the ability of the wires to carry heat away and dissipate it into air a few inches away. OTOH, a fire stop would be more constraining on the wires and could reduce the heat dissipation.
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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alt.engineering.electrical, snipped-for-privacy@ipal.net says...

Maybe I misunderstand incorrectly what a "fire stop" is here. I thought it was stuff to plug the holes so no air could move through the hole in the 2x. With the hole filled, the center of the wire is still only 3/4" from free air on either side of the 2x.
It seems silly to derate the wire, since that means more holes in the fire stop.
--
Keith

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| alt.engineering.electrical, snipped-for-privacy@ipal.net says...
|> | In article <37adfe4a-b085-4dd3-a291-
|> |> > I've searched all through my 2005 NEC looking for some guidance as to how |> |> > many 12/2 circuits I can run through a single 3/4" hole in the wall studs of |> |> > a house I'm building as a retirement project. I can not find anything about |> |> > it. I've also asked on several over groups. Is there some rule of thumb or |> |> > is there an actual regulation that I'm missing. I'm way out in the country |> |> > and we do not have an inspector that I can ask and the one in the county |> |> > seat said there is no restriction. I'm not concerned about county |> |> > restrictions, I'm concerned about safety. |> |> > |> |> > TIA |> |> > |> |> > -- |> |> > JC from Gnat Flats |> |> |> |> There are no rules on this in the 2005 NEC. As long as you keep the |> |> cables separated and not bundled and do not apply fire stopping you |> |> can put as many cables through a hole in a stud and will fit. |> |> If you apply fire stopping you must derate according to the 2008 NEC. |> | |> | Doesn't that seem sorta silly? |> |> No. A simple short (2 inches) hole does not tend to impact the ability |> of the wires to carry heat away and dissipate it into air a few inches |> away. OTOH, a fire stop would be more constraining on the wires and |> could reduce the heat dissipation. | | Maybe I misunderstand incorrectly what a "fire stop" is here. I | thought it was stuff to plug the holes so no air could move through | the hole in the 2x. With the hole filled, the center of the wire | is still only 3/4" from free air on either side of the 2x.
Without the fire stop, the ability to dissipate is my multiple means. It can dissipate _some_ within the hole, and _some_ through the wires to the free air away from the hole. The fire stop would have the effect of reducing or eliminating _one_ of these means of heat escape. That is, afterall, its design purpose.
| It seems silly to derate the wire, since that means more holes in | the fire stop.
More holes would be if you reduce the bundling rate to _avoid_ derating or as much derating. Otherwise it means using _larger_ wire that is treated as rated less. The latter might have to be the way to do it if the number of holes is an issue (as building construction code or safe engineering may dictate).
I think the derating could be more flexible, such as a variant rating factor for the length of the run, and the heat transfer capability of the containing material. But this can also get complex and would need to be one of those "under engineering supervision" things (where a PE puts his license on the line).
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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alt.engineering.electrical, snipped-for-privacy@ipal.net says...

It only limits the radial dissipation for 3/4" of the wire, I.e. not much.

If you have a constant load... Well, you finish the sentence.

Nonsense.
--
Keith

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